The phonology of sperm whale coda vowels

Sperm whales (Physeter macro-cephalus) communicate using series of clicks known as codas. In previous research, sperm whale codas have been shown to resemble human vowels acoustically. Based on the number of formants, two different coda quality categories have been described: a-codas and i-codas. In the present paper, we demonstrate that sperm whale codas not only resemble human vowels acoustically but also pattern like them along several linguistic dimensions. First, traditional count- and timing-based coda types interact with coda 'vowel' quality (a versus i). Second, a-codas are generally longer than i-codas. Third, the duration of i-codas has a bimodal distribution, showing a contrast between short i-codas and long ī-codas. Fourth, the baseline coda length differs across whales. And fifth, edge clicks mismatching their coda often match an adjacent coda, a phenomenon that resembles human coarticulation. All five properties have close parallels in the phonetics and phonology of human languages, suggesting independent evolution. Sperm whale coda vocalizations are thus highly complex and represent one of the closest parallels to human phonology of any analysed animal communication system.